This study targets a group of early -middle adolescents that is probably the least likely to be affected by school-based prevention approaches and that may be one of the highest risk groups available: substance abusing juvenile offenders. Although treatment programs for adolescent substance abusers have proliferated, there is minimal evidence of their efficacy. Hence it is important to develop promising treatment approaches and to carefully evaluate their effectiveness. In this regard, multisystemic therapy (Henggeler & Borduin, 1990) is a recently developed treatment approach that has shown considerable promise in the treatment of antisocial youths and multiproblem families. Across several controlled outcome studies, multisystemic therapy has produced change in adolescent antisocial behavior and key mediators of such behavior (e.g., family warmth and communication, association with deviant peers), and reductions in substance use have been observed in two recent studies. This application proposes to extend the external validity of multisystemic therapy by evaluating its efficacy in the treatment of substance abusing delinquents. Participants will include 112 13- to 15-year-old youths and their families referred from Charleston Department Of Youth Services. Youths meeting the screening criteria will be assigned at random either to the multisystemic treatment condition or to juvenile justice services as usual. Following treatment termination in the multisystemic condition, youths and families will be assigned randomly either to continued therapeutic monitoring or to no continued monitoring conditions. A comprehensive, rigorous, and multifaceted evaluation methodology will be used that has several distinct purposes. The primary purpose is to evaluate the short-term and long-term (6-mth, 1-yr) efficacy of multisystemic therapy to reduce the youths' substance use and other antisocial behavior and to ameliorate dysfunction in the youths' family relations, peer relations, and school performance. A second purpose is to evaluate factors that are associated with successful therapeutic gut-come. The third purpose is to examine the effects of continued therapeutic monitoring after termination from multisystemic treatment. The fourth purpose of the project is to provide an initial data base from which the secondary preventive function of multisystemic therapy can be assessed.